Electrolyte composition and method of electrolytically removing stock from workpiece



12, 1967 c. FAUST ETAL 3,357,905

ELECTROLYTE COMPOSITION AND METHOD OF ELECTROLYTICALLY REMOVING STOCK FROM WORKPIECE Filed March 28, 1960 5 Sheets-Sheet 1 INVENTOR CHAHLE 5 L. FAU 5 7194/0 BY OHN 5. Cl, //"/0/?D Dec. 12, 1967 c. L FAUST ETAL 3,357,905

ELECTROLYTE COMPOSLTION AND METHOD OF ELECTROLYTICALLY Filed March 28, 1960 REMOVING STOCK FROM WORKPIECE 5 Sheets-Sheet 5 VOLTAGE 7 CONTROL CUTTIN 6 RATE 64/ Q. 0 k 0" o 0 Z 3 '9 9 c n. 40 0 9 c r u 9A la! CURRENT DENSITY INVENTOR5 CHARLES L. FAUSTRhD JOHN E.CL/FFORD.

fbTTO/QNEXS- United States Patent ELECTROLYTE CGOSlTiON AND METHOD 0F ELECTRGLYTHCALLY REMOVHNG STOCK FROM WORKPIECE Charles L. Faust and .iohn E. Clifford, Columbus, Ohio, assignors, by mesne assignments, to The Cleveland Twist Drill Company, Cleveland, Ohio, a corporation of Ohio Fiied Mar. 28, 1960, Ser. No. 17,982 The portion of the term of the patent subsequent to June 7, 1977, has been disclaimed Claims. (Cl. 204-443) The present application is a continuation-in-part of our prior copending application, Ser. No. 577,015 now Patent No. 2,939,825.

This invention relates as indicated to electrolyte compositions for use in the electrolyte sharpening, shaping and finishing of metal bodies and particularly for the sharpening, shaping and finishing of composite metal bodies by electrolytic dissolution of such materials as anodes, preferably without physical and mechanical contact with another solid and without either electric spark or electric arc discharge.

In the art of shaping, sharpening and finishing, several non-mechanical (meaning free from pressure cutting, smearing, and tearing as caused by tools and. abrasive wheels or belts) methods have been developed and are in limited commercial use. They are: the electric discharge processes that erode away a metal surface by are or spark discharge from the metal to another electrode in a dielectric medium; electrolytic process in which the metal item to be ground is made anodic in contact with diamonds or other non-metallic abrasive on a metal cathode or in contact with a metal as cathode; and sonic or ultrasonic processes that cut by high frequency vibration of a metal with abrasive powder between it and the material to be cut.

All the above-mentioned non-mechanical processes have advantages and limitations. The electric discharge, sonic and ultrasonic methods are especially adapted to drilling small holes or forming small cavities in materials hard to pierce, drill or form by conventional methods of piercing with twist drills or for forming cavities with routers, reamers, etc. These methods have been explored for shaping and finishing, and are meeting with some industrial successes, but their limitations prevent them from fully meeting the extensive needs for grinding and shaping hard-to-grind materials that now can be cut or ground only by diamond wheels or cannot be cut without damage with abrasive wheels of any type now known.

Certain of the electric discharge processes, for example, operate at 25 volts or higher, cut at practical speeds that cause rough surfaces; or produce smooth surfaces at impractically slow cutting speeds; do not produce sharp edges at reasonable rates of metal removal; and have best application for drilling or producing cavities. Sonic and ultra sonic methods have found very limited uses other than in drilling and in forming of cavities. For the electric discharge, sonic and ultrasonic methods, the electrode disc or drilling tool wears away at a rate almost the same as that at which the work piece is cut away by the electrogrinding or the drilling action or the cavity forming action. The attiitional action on the important part of the machine adds to the cost through need for replacement because of change in contour and/ or wearing away of the cutter, and for shut-down time to make such changes.

The so-called electrolytic grinding process requires the use of a diamond (or other inert non-metallic, non-conducting abrasive or metal) in contact with the work made anodic in an electrolytically conducting, but substantially neutral solution, such as a solution of sodium silicate, or of sodium nitrate and sodium nitrite in water. The prior art teaches the need for diamond (or other abrasive) 3,357,995 Patented Dec. 12, 1967 wheels or discs for two major reasons: (1) the protruding diamonds act as spacers touching the surface of the article to be finished so as to automatically maintain spacing that fixes the thickness of electrolyte film; and (2) to scrape away from the surface the insoluble salts or oxides that form on and adhere to the surface of the article being finished. By these two requirements, the prior art limits the cutting rate (rate of metal removal) because: the non-conducting diamonds reduce the active cathode area and the maximum current is limited to correspond to a lower anode current density than if the diamonds were absent and the conducting area were increased by the amount of area occupied by the diamonds; the diamonds further decrease the maximum operating current by restricting electrolyte flow over the cathode surface so there is polarization in the electrolyte-filled valleys and electrolysis current flow is limited; or the metal-removal rate is limited to the current flow that forms solid adhering anode products at a rate just equal to that at which the products are scraped away by the diamonds.

In the electrolytic sharpening, shaping, and finishing of certain conductive materials, such as the hard dense carbides or composite articles composed of several metals, additional problems arise. For example, in cemented tungsten carbide, not only does the insoluble oxide of tungsten form on the surface of the anode, but compounds of the cementing agent, usually cobalt, also similarly form. Even where such interfering oxide films are not scraped away as by the known, described diamond wheel but are solubilized in accordance with the present invention, it is emphasized that the solubilizing agents which are effective on tungsten oxide are not necessarily effective on cobalt oxide.

Moreover, in a common example of a cutting tool, cemented tungsten carbide is brazed as by solder to one end of a shank of steel. If such an assembly is subjected to electrolytic grinding action, the various metals present are electrolytically dissolved at appreciably diiferent rates. Thus, the electrolytic dissolution of a composite anode can be considered as composed of three electrode processes occurring simultaneously. It has been calculated that, assuming a current density distribution to be uniform over the anode face (for example about 50 amperes per square inch) and assuming that each electrode process is percent efficient, the respective cutting rates for the carbide, steel, and brazing alloy will be 2.5X10- 6.8 1O and 12.5 x10 inch per minute. This difference in rates is, of course, undesirable and shows that the cutting rate of the carbide is a limting factor when using a composite anode.

A further important factor in any electro-process for the removal of metal stock is the current density employed. In tests with a diamond wheel and using a very small gap, a current density of about 350 amperes per square inch at 15 volts was the limiting value because of sparking. Sparking, of course, is undesirable, since it not only represents loss of current efliciency (part of the current flow is not dissolving metal), but sparking also causes erosion of the cathode. In comparison, using an electrolyte composition of the present invention, a current density of 425 amperes per square inch at 25 volts was reached without parking. This emphasizes that the limiting current density is more dependent on the type of electrolyte used than on the mechanical features of the process. As a direct benefit, we have been able to produce a sharper edge at a higher current density (higher cutting rate). The 0pposite relationship is reported for the electrolytically assisted diamond-grinding process. Further, the surface finish obtained at our higher cutting rate is as good as that obtained at the lower cutting rate. This is not true, for example, in the electrospark process.

In distinction to the foregoing, the present invention has shown that cutting or metal-removal rates by anodic electrolysis can greatly exceed those reached by the aforementioned non-mechanical methods, without mechanical action by or physical contact with the article being electrolytically ground or machined. This is electrolytic grind ing in its true coulombic meaning without mechanical contact and/or action. As such term is used herein, electrolytic grinding is taken to mean sharpening, shaping, and finishing of a workpiece without actually mechanically contacting it. Consequently, surfaces are smooth, no stresses of any kind are induced into the surface of the article being shaped or finished, and hardness or composition of the metal or electrically conducting material has no significance. Voltages are 25 volts or less and are usually 4 to 8 volts, which are so low as to be without danger to machine operators. As is described hereinafter, it has been shown that meta-ls and electrically conducting materials can be electrolytically ground at speeds at least twice those at which diamond wheels can grind such mate rials as cemented tungsten carbide.

The present invention further includes specific electrolyte compositions which we have developed to overcome the described problems of anodic coatings including polarization, such as for tungsten carbide, to provide substantially equal dissolution rates for composite metal articles, and to provide relatively high current densities.

It is a primary object of this invention, therefore, to provide methods and apparatus for electrolytically sharpening, shaping, and finishing metals and other electrically conducting materials without mechanical action or physical contact of any kind.

It is another object of this invention to provide methods of and apparatus for shaping, sharpening, and finishing metals and electrically conducting materials without generation of damaging heat, introduction of stresses from pressure, mechanical work, or electric discharge.

It is a further object to provide improved electrolyte compositions generally applicable to electro-process for the removal of metal stock from cemented tungsten carbide and particularly applicable for the method and apparatus herein disclosed.

It is a still further object to provide such electrolyte composition to prevent the formation of insoluble films of metal compounds which form along the anode metal being so electrolytically sharpened, shaped, and finished.

It is a still further object to provide electrolyte compositions which afford simultaneously electrolytic grinding of the metal of a composite article and at substantially equal and rapid rates, for example, cobalt-cemented tungsten carbide inserts brazed to tool steel by silver solder, so as to provide a sharp edge on the carbide.

It is a still further object to provide electrolyte compositions which afford relatively high current densities for electro-processes for the removal of metal stock.

Other objects and advantages of the present invention will become apparent a the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

In the annexed drawings:

FIG. 1 is a perspective view of one form of apparatus which may be used in conjunction with the electrolyte compositions of our invention;

FIG. 2 is a perspective view partially in section and drawn to an enlarged scale of a portion of the apparatus illustrated in FIG. 1 showing in greater detail the cathode disk on which the electrolyte is supported and to which is presented the body to be electrolytically ground;

FIG. 3 is an enlarged fragmentary view of a portion of the assemblage illustrated in FIG. 2 showing in greater particularity the physical relationship between the cathode, anode and the electrolyte solution therebetween;

FIG. 4 is an illustration of an alternative form of apparatus by which the method of this invention may be carried out;

FIG. 5 is a graph showing the effect of anode-to-cathode spacing on the current density and cutting rate when the method of this invention is used for electrolytically grinding cemented tungsten carbide;

FIG. 6 is a similar graph when the object electrolytically ground is made of high vanadium carbon tool steel;

FIG. 7 is a diagrammatic representation of one method of controlling the spacing between the anodic workpiece and the cathode; and

FIG. 8 is a graph showing the general relationship between current density, cutting rate and spacing between the anode and cathode at various voltages.

Although the present electrolyte compositions are of general application in electro-processes for the removal of metal stock, the compositions are particularly designed for use with the method and apparatus described in our copending application, Serial No. 577,015 now Patent No. 2,939,825. Therefore, the electrolyte compositions are disclosed in connection with the method and apparatus of our cited application. As more fully described and claimed therein, the preferred method for use in conjunction with the present electrolyte compositions comprises:

(a) Providing an electrolyte in which a metal body is electrolytically soluble;

(-b) Relatively moving the body, as an anode, substantially in surface contact with a continuous layer of the electrolyte, which is supported on a cathode in spaced relation to the anode;

(c) While maintaining a direct current flow between the body and electrolyte;

(d) Such method characterized further in that said anode and cathode are at all times in physical spaced relation.

By the term electrolytic dissolution as used throughout this description and in the claims is meant the substantial complete dissolution progressively of the surface of a material according to Faradays law.

When metals or electrically conducting materials are made anodic in electrolytic solutions in such conventional processes as electroplating and electropolishing, dissolution rate depends on the current density that can be maintained without polarization of the anode or the cathode. Polarization increases resistance to flow of electric current so that electrolysis current decreases and dissolution rate falls off, or a higher applied voltage is required. For any electrolyte, there is a maximum voltage above which further increase will not cause the required electric current flow for a given metal anode and indeed may even cause current to cease to flow because of the formation of an insoluble film of oxide or salt on the metal anode surface. Because of polarization, dissolution rates of anodes are slow relative to the metal removal rate needed for practical grinding and shaping of metals in machine shop practices. By electrolysis as in plating, electroetching, or electropolishing, metal dissolution rates do not exceed 0.05 to 0.1 inch per hour. Other investigators have increased electrolytic dissolution by means of mechanical assistance given by electrically conducting abrasive wheels in contact with the article being electrolytically ground so as to continuously scrape away insulating salt or oxide coatings, and thereby, provide for continuous high-current density anodic dissolution. For example, Keeleric, and others using his process, passed direct current through cemented tungsten carbide and achieved substantial metal removal rates only because of scraping action of an electrically conducting diamond grinding wheel touching thesurface of the cemented carbide. Thus, Keeleric effected a significant improvement in anodic dissolution for grinding and shaping. But, the Keeleric method, as do others known as electrolytic grinding, depends on physical con;

tact and scraping or even actual abrasive cutting simultaneously and requires costly diamond wheels which are electrically conductive and a special design. Any process which depends upon physical contact or abrasive cutting may result in a damaging heating of the work. Furthermore, effectiveness of such a process, depending on scraping and/ or abrasive cutting, is limited in maximum cutting rate to those conditions of relative rate of film formation and removal by scraping.

A significant and greater increase in electrolytic grinding rate would be attained if solid film formation was avoided and the need for scraping or physical contact with abrasive or rubbing surface accordingly eliminated. Such an accomplishment is realized by very accurate control of the film thickness of electrolyte solution supplied at very high flow rate across the surface of a metal to be ground or shaped and used as an anode. By this method, commercially practical grinding or cutting rates of metalremoval are accomplished without spark or are discharge. The dissolution is strictly electrolytic in the coulombic meaning. In this manner, cemented tungsten acrbide has been cut at a metal-removal rate of 0.057 inch per minute at 1550 amperes per square inch at 76 percent anodic current efliciency, or at a rate of 0.040 inch per minute at 800 amperes per square inch at 100 percent anode efliciency.

It is not unexpected that technical and patent literature described processes in which scraping or abrasive assistance is required for electrolytically grinding cemented tungsten carbide. Most usually, the cementing metal is cobalt. Tungsten oxide is well-known to be soluble in alkaline solutions and insoluble in acid solutions. Cobalt oxide is insoluble in alkaline and soluble in acid solutions. Oxides of both metals are insoluble in neutral solutions. Polarization causes metal oxide films to form on anodes when limiting current densities are exceeded. Limiting current densities are much too low for tungsten carbide cemented with cobalt in simple acid, neutral or alkaline solutions for practical electrolytic grinding rates without scraping to remove either tungsten oxide or cobalt oxide, depending on whether the electrolyte is acid or alkaline. When utilizing methods which depend on scraping of the anode face, one disadvantage is that control is diflieult and critical for maintaining light Wheel contact, while yet avoiding pressure that introduces cutting by the abrasive and thus wheel wear also, as well as producing a damaging heating of the work.

By the method of the present invention cobalt-cemented tungsten carbide can be electrolytically ground or cut at high metal-removal rate without abrasive wheel or other wheel contact by using an alkaline solution of an electrolyte in which tungsten oxide is very soluble and which contains a solubilizing or complexing agent for the cobalt. Preferably, in addition the electrolyte solution must be replaced at a high rate at the anode face. Such replacement can be effected in a satisfactory manner by distributing the electrolyte in a layer less than 0.020 inch and usually less than 0.008 inch in thickness on a rotating cathode disk as hereinafter described.

As previously indicated, the present development is directed to improved electrolyte compositions primarily for the electrolytic removal of tungsten carbide stock, such as in single point masonry drills, and especially for the electrolytic treatment of composite articles of cemented tungsten carbide and steel in which a number of metals are simultaneously subjected to electrolytic dissolution.

The problem of electrolytically grinding several different metals simultaneously as for tool sharpening is very complex because of the large number of variables in the process. Preferably, each metal should be cut level to within 0.001 inch of each other. The overall metal re-- moval rate from the ground surface is preferably at least 0.005 inch per minute to be practical. A surface finish of about RMS (root mean square) microinch or better for the carbide and about 25 RMS microinch for the steel are desirable. The flatness of cut and carbide-edge sharp ness preferably approaches that attainable in conventional grinding.

The present electrolyte compositions provide acceptable high rates of dissolution without scraping of the workpiece as by a diamond wheel. It is understood that by tungsten carbide, we include the commercial grades thereof which include minor impurities or additions such as titanium carbide and molybdenum carbide.

In accordance with the present development, we employ a multi-cornponent electrolyte tailored to meet diverse requirements in the electrolytic dissolution of metals, particularly cemented tungsten carbide alone or present in composite articles including steel and/ or solder.

An essential component of all of the present electrolytes for use with tungsten carbide is an ionizable hydroxide compound which is soluble in the medium employed to make the electrolyte solution. In addition to making the electrolyte solution electrolytically conductive, this ionizable hydroxide compound also includes an anion that promotes anodic activity at current densities and voltages needed for practicing the invention and, particularly, an anion that solubilizes the tungsten, usually in the form of an oxide, that is released as a result of the electrolytic dissolution.

A tungsten carbide workpiece is usually cemented as by the metal cobalt. With just the ionizable hydroxide compound present, the cobalt would precipitate by hydrolysis during the electrolytic dissolution to form basic cobalt salts or cobalt hydroxide at the very moment the cobalt is released from the workpiece as an ion. The cobalt ion is immediately adjacent the workpiece surface and tends to insulate such surface. Accordingly, it becomes necessary to add a further ingredient to solubilize or form a complex with the cobalt which is usually also in the form of the oxide. The ingredient added to solubilize the cobalt may or may not itself be ionizaole. We have discovered two broad groups which are effective for this purpose in combination with the described hydroxide compound. One group comprises a salt of a saturated polybasic aliphatic organic acid and, more particularly, a water soluble salt of such an acid since water is commonly used as the solvent to the electrolyte. Specific examples of this group include a tartrate, a citrate, an oxalate, and a gluconate. In this regard, it will be noted that for the purposes of the disclosure and appended claims we are defining gluconic acid as a polybasic acid (in distinction from a monobasic acid) as so considered by L. F. Fieser and M. Fieser in their text Organic Chemistry, D. C. Heath and Company, 1944, page 464. It will also be noted that tartaric, citric, and gluconic acids are hy droxy acids and, further, that oxalic acid when hydrated may be similarly considered to be a hydroxy acid. The second group comprises compounds containing nitrogen and, more particularly, an ammonium halide and an organic amine. Specific examples of this group include am monium chloride, ammonium fluoride, ammonium iodide, and ammonium bromide as the ammonium halides; and an alkaline amine, such as triethanolamine, ethylenediamine, and tetrasodium ethylenediaminetetraacetate, etc. as the organic amine.

With the cobalt complexers of the first group, the use of the chloride ionis optional to enhance cutting of the carbide. The chloride ion has the advantage of additionally improving the surface of the electrolytically shaped carbide. However, if tungsten carbide and steel are to be jointly electrolytically shaped, a halogen is added to the foregoing formulations such as the chloride, fluoride, bromide, and iodide ions. The fluoride, bromide, and iodide ions are not as effective as the chloride ion, and therefore the latter is preferred. The addition of a halogen is preferably carried out by a salt soluble in the electrolyte solution. For example, the sodium, ammonium, potassium and lithium salts and the like may be used with water.

Further, if silver solder is present in a composite metal article and is also to be cut or electrolytically shaped or dissolved along with the other metals, a solubilizer or complexer must be added for the solder. Solubilizers effective for this purpose include a water-soluble cyanide, ethylenediamine, and tetrasodium ethylenediaminetetraacetate. The water-soluble cyanide, in turn, may include the sodium, potassium, ammonium, and lithium cyanides.

From the foregoing, it will be apparent that the anions of the various components of the electrolyte are the critical portions of the electrolyte insofar as obtaining the results desired in accordance with the present invention.

About the only requirements for the cation is that when chemically bound with the anion, the resulting compound is soluble in the medium selected for the electrolytic removal and is not otherwise reactive with the surrounding environment. Since the medium is virtually without exception always Water, it is thus only necessary that the electrolyte be water-soluble. In the examples hereinafter given, the electrolytes are often listed with sodium as the cation, since such compounds are usually most available, less expensive, etc., and therefore most often employed. However, any compound furnishing the desired anions and soluble in the solvent of the electrolyte solution is within the contemplation of the invention. For example, the potassium, lithium, ammonium and other compounds of the anions herein described when soluble in the medium employed are also applicable.

Although as just noted, the cations of the ingredients of the electrolyte are not as important or critical as the anions, one exception appears in the case of the arnmonium cation. The ammonium ion is important in the electrolytic dissolution of cobalt-cemented tungsten carbide, since ammonium forms ions of various cobaltic complexes such as the hexamminecobaltic ion [Co(NH the chloropentamminecobaltic ion, [Co(NH Cl]++; or the dichlorotetraamminecobaltic ion, [Co(NH ).,Cl Thus, our experimental work indicated that both the ammonium and halide ions such as chloride ions were needed for solubilizing cobalt where this complexing agent is employed. Neither the combination of sodium hydroxide and sodium chloride nor the combination of sodium hydroxide and ammonium hydroxide Was effective in electrolytically shaping cobalt-cemented carbide. However, as noted the combination of sodium hydroxide and ammonium chloride was effective. The ammonium ion appears to be the exception where a chloride or other halogen ion is essential to obtain any electrolytic shaping of cemented carbide. Accordingly, while the simultaneous presence of an ammonium and halogen ion is necessary in this form of the invention, it is apparent that the combination of ammonium and a halogen ion such as the chloride ion could be obtained also by adding sodium chloride to a mixture of sodium hydroxide and ammonium hydroxide, or by adding ammonium hydroxide to a mixture of sodium hydroxide and sodium chloride, etc. It is emphasized therefore that the claiming of an ammonium halide in the claims is intended to include the conjoint presence of ammonium and halide ions, however derived. In short, the term ammonium halide means any combination of chemicals which in solution provides the ammonium and halide ions. In this manner the ammonium ion can be provided from compounds like ammonium hydroxide, ammonium sulfate, and ammonium nitrate.

The amounts of the various possible ingredients of the present electrolytes have not been found to be critical. Obviously, a sufficient amount of an ionizable material or materials is needed to efiect the passing of a current. Likewise, a suflicient amount of a solubilizing component should be used to accommodate the amount of each metal or metal compound electrolyticmly dissolved from the workpiece for which the solubilizer component is designed. Since the amount of such metal or metal compound present will vary, it follows that the amount of the solubilizing component can vary also. The actual amounts needed are easily determined by trial and error.

As a general guide to amounts which may be used, the following may be considered:

(1) For cemented carbide alone the range of the compound furnishiug hydroxyl ions is virtually Without limit, a minimum being required to conduct a current. The amount of complexing agent needed for the cobalt is somewhat proportional to the percentage of the cobalt binder in the cemented carbide.

(2) For cutting cemented carbide and steel simultaneously:

(a) The addition of the chloride ion (or halogen equivalent) is advisable.

(b) The range of the compound furnishing the hydroxyl ions is somewhat reduced.

(c) The relative amounts of complexing agents required for cemented carbide and steel depend on the relative areas of the carbide and steel which are cut simultaneously (the ratio was 1:1 in experimental work). Thus, the composition examples will vary where the ratios of carbon and steel surfaces also vary.

(3) For cutting carbide, steel, and silver solder which requires the further addition of a complexing agent for the solder as previously noted, the percentage of the added complexing agent depends also on the area of the silver solder exposed. In the experimental Work in which the following formulations were used, the area of the exposed workpiece include about 48 percent cemented carbide, 48 percent steel and 4 percent silver solder.

In the following examples, ranges of amounts especially found to be operable are given more fully to illustrate the invention. As shown by Examples I to XXII, the electrolyte which provides the electrolytic action may range from about 0.5 to about 200 grams per liter of solution. All examples given had an aqueous solvent. These examples illustrate electrolyte compositions in which the hydroxyl ion is obtained from compounds representing the ionizable component and also illustrate the solubilizing agent or agents that may be used therewith.

EXAMPLE I Grams per liter Sodium hydroxide 45 to 60 Ammonium chloride 50 to 150 EXAMPLE II Grams per liter Sodium hydroxide 45 to 60 Sodium chloride 100 to 200 Ethylene diamine 40 to Carbide was cut or electrolytically dissolved, although steel did not cut as fast as the carbide.

In place of sodium citrate, an amount of ammonium citrate could be used which furnished an equimolar amount of the citrate ion.

EXAMPLE V Grams per liter Sodium hydroxide 60 to Tetrasodium ethylenediamine-tetraacetate 30 to The tetrasodium compound is used to solubilize cobalt oxide.

9 EXAMPLE VI Grams per liter Sodium hydroxide 10 to 100 Sodium chloride 5 to 150 Alkaline amine 50 to 300 When the alkaline amine is triethanolamine, the fastest cutting rate for tungsten carbide is obtained when the ratio (in grams per liter) of triethanolamine to sodium hydroxide is about unity and about the minimum quantity indicated for sodium chloride is present. When the concentration of triethanolamine and sodium hydroxide is low (about 50 grams per liter), a high cutting rate is obtained but the surface is uneven. As the concentration is increased, the surface becomes more level and the finish improves. However, the cutting rate decreases with greater than about 150 g./ 1. of sodium hydroxide and about 15 g./l. of triethanolamine.

EXAMPLE VII Grams per liter Sodium hydroxide 50 to 100 Sodium chloride 50 to 100 Triethanolamine 50 to 260 Sodium cyanide to 35 This electrolyte did not show any rusting action on steel and provided tungsten carbide with a surface finish of 5 RMS microinches.

EXAMPLE VIII Grams per liter Sodium tartrate 25 to 170 Sodium hydroxide 20 to 150 Sodium chloride 0 to 50 Electrolytes containing the tartrate radical are especially recommended for grinding carbide tools, since these electrolytes are not corrosive and no special materials or construction are required. Thus, these electrolytes may be used for grinding either tungsten carbide alone or composite articles of tungsten carbide with steel.

EXAMPLE IX Grams per liter Sodium tartrate 50 to 170 Sodium hydroxide 60 to 150 Sodium chloride to 50 Ethylene diamine 5 to 35 The electrolyte initially contained sodium tartrate (42 grams per liter) and sodium hydroxide (60 grams per liter). As the concentration of tartrate was increased, the current density and cutting rate decreased, but the surface of the carbide did not improve. Steel was not cut with the electrolyte as constituted at this point.

When sodium was added, the steel cut at a high rate of 0.016 inch per minute and the carbide at 0.019 inch per minute. The carbide became smooth and shiny after adding the chloride, but the leading edge was less sharp. The steel surface was rough but slightly better than obtained with the triethanolamine electrolyte. Ethylene diamine was added to cut the brazing alloy, and a composite anode was cut at 0.028 inch per minute.

A composite amount of tungsten carbide and steel was cut at 0.021 inch/minute based on the carbide; the steel did not cut as fast and was not as smooth.

EXAMPLE XI While the chloride ion is the preferred halogen ion, the fluoride, bromide, andiodide ions are also effective to a de ree. Of the four halogens, the chloride ion gives the best appearance to the electrolytically shaped workpiece.

Triethanolamine 197 Potassium hydroxide 70 Potassium cyanide 33 Potassium fluoride EXAMPLE XII The following is an equimolar comparison of chloride and iodide:

Sodium tartrate, g./l 105 Sodium hydroxide, g./l 30 30 Sodium iodide, g./l 69 Sodium chloride, g./l 25 Carbide, inch/minute 0.003 0.012 Steel, inch/minute 0.002 0.005

EXAMPLE XIII G./l. Sodium tartrate 50 to 170 Sodium hydroxide 60 to Sodium chloride 15 to 50 Tetrasodium ethylenediamine tetraacetate 5 to 35 EXAMPLE XIV Ammonium oxalate 80 Sodium oxalate 35 Ammonium chloride 40 Sodium hydroxide 23 Sodium cyanide 25 EXAMPLE XV Triethanolamine 50 to 200 Sodium hydroxide 50 to 100 Sodium chloride 50 to 150 Sodium cyanide 5 to 35 Sodium carbonate 5to 3.5

This composition is particularly well suited to the electrolytic dissolution of cobalt-cemented tungsten carbide soldered by silver solder to steel. The hydroxyl serves to solubilize the tungsten oxide formed; the triethanolmine serves to solubilize the colbalt oxide formed; the chloride anion serves to prevent anodic polarization on the carbide workpiece; the cyanide anion serves to solubilize the electrolytically dissolved silver solder; and the sodium carbonate improves the appearance of the electrolytically treated steel. The sodium carbonate not only improved the steel surface but also that of the carbide surface with regard to flatness and edge sharpness.

EXAMPLE XVI The following are the conditions for one specific electrolytic dissolution operation in which the lip clearance and outside diameter of a %-inch tungsten carbide masonry drill were electrolytically ground.

Electrolyte composition:

Sodium tartrate .grams per liter-.. 168 Sodium hydroxide do 150 Sodium chloride do 25 Voltage, volts 5 Current density, amperes per square inch 800 Cathode-wheel speed, feet per minute 6000 Cutting rate, inch per minute (approximately) 0.020 Surface finish, microinches RMS (estimated) 10 EXAMPLE XVII The following are the conditions for a further electrolytic dissolution operation in which three metals were simultaneously electrolytically ground. These metals include cemented tungsten carbide (6% cobalt), a brazing 11 alloy (Eazy Flo No. 3 Handy and Harman), and steel (Momax).

Electrolyte composition:

Sodium tartrate grams per liter 168 Sodium hydroxide d 60 Sodium chloride do 50 Voltage, volts 5 Current density, amperes per square inch (approximately) 300 Cutting rate, inch per minute 0.010 to 0.020

Surface finish, microinches RMS (estimated) EXAMPLE XVIII This electrolyte was used for vanadium steel:

G./l. Sodium chloride 12.5 to 200 Boric acid 1.25 to 25 A pH within the range of 1.8 to 10 may be used, a pH of 7 or higher being preferred. The boric acid buffered the pH around the neutral point. In cutting steel at high current density, the buffering performs a very important function of preventing the pH from increasing. Many problems are encountered in trying to cut steel in the alkaline solution needed for the carbide and these are alleviated or eliminated by the use of the bufiering agent. Preferably the ratio of sodium chloride to boric acid is maintained at 10:1, while the concentrations vary within the range shown. Good cutting results on vanadium steel were obtained with all concentrations. One composition that was efiective on shank steel, Momax, as well as vanadium steel was:

G./l. Sodium chloride 200 Boric acid 25 EXAMPLE XIX Cemented tungsten carbide was plunge ground electrolytically in the following aqueous electrolyte:

Grams per liter Sodium tartrate 150 Sodium hydroxide 150 Sodium chloride 20 The cutting rate in inch per minute as shown in FIG. 5 Was substantially directly proportional to the anode (the article being ground) current density, which also was substantially indirectly proportional to the anode-to-cathode spacing which is the effective thickness of electrolyte film. The dotted line shows the theoretical cutting rate of 100 percent current efficiency. At current density above 1000 amperes per square inch, the actual efliciency appears slightly less than 100 percent, indicating that some polarization did occur; but even so, the high anode efliciencies shown by this example have not heretofore been attained at current densities over a few hundred amperes per square foot, thus attesting to a novel accomplishment by the present invention.

The importance of establishing very high current density is shown by the appearance of the carbide surface at several levels of the current density range covered by FIG. 5. 1

Current density ran ge smooth than surface at 501 to 1150 amp/sq. in.

For some applications, very sharp edges are desired such as those resulting from diamond-wheel grinding to sharpen cutting tools. The very high current densities shown in FIG. 5 for Example XIX can occur only because cathode polarization is essentially eliminated by the high rate of electrolyte flow through the cutting gap which sweeps away the hydrogen (principal product at the cathode disk surface) at the instant it forms. The slight fall oil in efliciency at the high current density end of the range shown in FIG. 5 indicates that some anode polarization may have occurred. Clearly also at the 25-volt operation, polarization at the edges was slightly less than at the rest of the surface being dissolved, so some edge rounding occurred. This is desirable for the smooth running of some engine and other mechanism parts, but is not desirable when a very sharp edge is desired as in sharpening a cutting tool.

Since the agitation for anodic dissolution in the electrolysis gap clearly reached heretofore unheard-of agitation rate by streamline flow, permitting exceptionally high current densities, electrolysis at some lower voltage should take place, so that a slight decrease in agitation should cause a relatively large decrease in current density, and thus a large decrease in metal-removal rate. Because of the firmness of the electrolyte film on the cathode disk, there is no pile-up of electrolyte on the leading edge of the article being ground to the detriment of sharpening. Thus, in the absence of turbulence, the agitation effect is slightly less on a part of the article not substantially parallel to electrolyte flow. This slight difference in agitation at an edge is not enough to cause the decreased current density resulting from less agitation to offset the greater current at edges caused by normal current distribution at 25 volts. In the electrolyte film, as provided by the present technique, it was found that at 5 volts direct current, the slightly less agitation at the edges caused lesser current density that offset the increase that configuration would give current distribution to effect greater current density and metal removal at edges. So with conditions the same as for Example XIX except at 5 volts applied EMF, the edges were as sharp as those produced by diamond- Wheel grinding.

The process described herein for electrolytic grinding is eminently suitable for grinding materials other than cemented carbide. Since the process does not remove metal by mechanically cutting it away, hardness is no factor in electrolytic grinding. Thus, metals of widely difierent hardnesses can be electrolytically ground simultaneously; for example, cemented tungsten carbide, silver solder, and tool steel; and with the instant electrolyte solutions, they can be ground at substantially the same rates. Such a combination now requires tedious and careful grinding with diamond wheels and with wheels of less costly abrasives. Care must be taken not to grind silver solder and steel with the diamond wheels, and the wheel of other abrasives used to cut the silver solder and steel is Worn excessively if it contacts the cemented tungsten carbide.

EXAMPLE XX Since it is not practical to use a diamond wheel or an abrasive wheel of other type for the complete grinding and shaping of cemented tungsten carbide, silver solder and tool steel, a method for grinding all three at once is both novel and practical. All three metals were simultaneously electrolytically ground in thin film electrolytes of the following compositioni n the electrolytic grinding unit shown in FIG. 1.

Grams per liter Triethanolamine 197 Sodium Hydroxide 50 Sodium Chloride Sodium Cyanide 25 Sodium Carbonate 25 Sodium Tartrate 105 Sodium Hydroxide 60 Sodium Chloride 50 Ethylenediamine 25 Current density amp./sq. in. 300 Cathode wheel speed ft./min. 6000 Anode area sq. in 0.2 Anode-to-cathode space in 0.002

Both electrolytes gave approximately the same results for electrolytic grinding at 25 volts. Cutting rate was 0.020 inch per minute; the carbide surface was smooth to RMS microinches), but was slightly wavy and the edges were slightly round; and the steel had a surface finish of 70 to 100 microinches.

Electrolytic grinding at 5 volts produced a fiat, nonwavy tungsten carbide surface with sharp edges and a smooth polished finish on the steel and silver solder.

The electrolyte flow system and rotating disk remain the same for presenting a thin, electrolyte film to the article to be ground. Because the electrode reaction of different metals differs at high current densities, and the solubilities of metal oxides and salts differ, the best electrolytic grinding results will require some changes in electrolyte for different metals. Note that electrolytes A and B of this example differ in composition from the electrolyte of Example XIX. The cyanide in A and ethylenediamine in B effects dissolution of the silver solder and the chloride prevents anodic polarization of the steel, solubilization of which in alkaline solution is effected by the triethanolamine or the tartrate, both of which are equally effective in allowing high current density, high efficiency dissolution of the cobalt.

For simultaneously electrolytic grinding cemented tungsten carbide, silver solder and tool steel at 5 volts applied EMF, the use of ethylenediamine for the solder is optional if the silver solder area is a relatively small part of the total anode area. For example, the electrolyte can comprise:

Grams per liter Sodium tartrate 168 Sodium hydroxide 60 Sodium chloride 50 At 300 amperes per square inch, 6000 feet per minute disk speed (FIG. 1) and lowest electrolyte flow that gave uniform film, metal-removal rate was 0.020 inch per minute and surface finish was 10 RMS microinches on what as the percent cobalt is different or as nickel or other cementing metals are used.

EXAMPLE XXI High vanadium carbon tool steel was also electrolytically ground at high rates by the technique of this invention. An electrolyte consisting of an aqueous solution of 200 g./l. sodium chloride and 25 g./'l. boric acid was used. At cathode disk speed of 6000 feet per minute, 25 volts applied EMF, cutting rates of 0.010 to 0.140 inch per minute were attained depending on the anodeto-cathode gap (i.e., the electrolyte film thickness) as shown in FIG. 6. Projection of the line for anode-tocathode spacing shows an electrolytic cutting rate of about 0.165 inch per minute at 0.001 inch spacing.

Low-alloy steels, high and low carbon steels, and stainless steels can be electrolytically ground under the conditions cited for this example. Cutting rates are substantially the same for all. Very little difference is seen in cutting rates as pH varies from 1.8 to 10. Finish appearance is slightly better at pH of 7 and higher.

At 5 volts, electrolytic cutting rate is slightly slower than at 25 volts, but surface finish is better for some metals. Thus, a roughing out can be taken at the higher voltage for speed and finishing can be done for appearance at the low voltage. The only change is in voltage regulation, Whereas, for abrasive wheel grinding either the Wheel must be changed or the work must be reset-up on a second machine for finishing after rough cutting.

The aspect of variability of voltage is a characteristic of electrolytes having good conductance and high solubility for metal oxides and anodic oxidation of metal compounds with non-metals such as represented by tungsten carbide. Thus, a feature of the present process is the use of an electrolyte composition giving good electrical conductance and having high solubility for metal oxides and for salts of the anions in the electrolyte and the metal dissolved during the electrolytic grinding.

EXAMPLE XXII The salts of the saturated polybasic aliphatic organic acids can be formed by adding the acid itself to an alkaline solution. However, the substitution of the acid for the acid salt must be on a molar basis, and an excess of alkali must be provided to utilize the acid and leave the desired concentration of free alkali. For example, the following electrolyte composition is equivalent to that given for Example XVII.

Grams per liter Sodium hydroxide 1292 Tartaric acid Sodium chloride so Electrolyte compositions for carrying out the process defined herein have the chemical ability to solubilize the oxides of the metals and the metallic elements being processed. For example, electrolytically grinding a part consisting of cemented tungsten carbide, silver solder and tool steel requires that tungsten oxide, cobalt oxide, oxides of silver, copper, zinc, cadmium, and nickel, such metals being constituents of the solder, and iron oxides be dissolved. As earlier noted, tungsten oxide is soluble in alkaline solutions and insoluble in acid solutions; cobalt oxide and iron oxide are insoluble in alkaline solutions but soluble in acid solutions. In electrolytes of this invention, the oxides of all the metals named are soluble because of special improvements present in an alkaline solution. The electrolyte of Example IX, for example, contains sodium hydroxide to dissolve the tungsten electrolytically, sodium tartrate to make the cobalt soluble and sodium tartrate plus sodium chloride to make the iron soluble. The ethylene diamine in this example provides solubility for silver solder when the operating voltage is high enough to cause polarization of the silver. When the operating voltage is low enough to avoid polarization, the ethylene diamine is not needed and the electrolyte of Example VIII will electrolytically carry out the process described for a combination of the three metallic components.

For metallic elements that are substantially steel with minor alloying constituents, chloride solutions provide sufiicient solubility for the oxides and are, therefore, useful for electrolytic grinding as described herein.

Or, in the case of an alloy, the electrolyte can be selected for dissolving characteristics of the major constituent and by dissolving it permit the alloying elements to fall free without need for electrolytic solubility or mechanical scraping.

In the absence of the oxidizing effect of the electric current passed through the metallic components as anodes, these electrolytes are without substantial attack upon the metallic components. With the passage of the electric current as described herein, the metallic components are dissolved at substantial current efficiencies according to Faradays law. While the operations are technically feasible at any current efliciency for metal dissolution, we prefer to operate at values above 40% current efficiency. The balance of the electro process which makes the current efliciency total to 100 is believed to be consumed in dissociating water with the discharge of oxygen simultaneously with the metal dissolution that brings about the electrolytic grinding. For the most practical operations, current eificiencies will exceed 80% for metal dissolution.

Generally electrolytic processes have limiting current densities, such that increase in current density beyond this point effects no further increase in the rate of metal dissolution. This condition is reached when the rate of metal dissolution just equals the rate at which the dissolved metal ion can be accepted by the solubilizing ions and the product can diffuse away while at the same time new acceptor ions can diffuse to the metal surface. This limiting current density condition involves a diifusion layer at the anode surface that has a thickness in the range of a bout 0.005 inch. The only way to speed up the anodic dissolution is to exceed the limiting current density by disturbing the naturally-forming diffusion layer so that the products of dissolution are swept away and fresh dissolving solution is supplied at a rate faster than normal diffusion can maintain. Thus, by flowing electrolyte under forced pressure into the gap between the two electrodes, as hereinafter more fully described, the products of dissolution are swept out and fresh solution is supplied at the high rate necessary for maintaining high-speed anodic dissolution. Thus, there is a minimum speed of fresh flow in the gap between the electrodes that will correspond with or be greater than the normal diffusion film thickness. There can be an excessive amount of turbulence at the metal surface such that the diffusion film is broken up into globules of liquid and does not maintain a continuous liquid layer in contact with the anode surface. The rate of anodic dissolution will be decreased approximately by the amount that the contact area of anode to liquid is decreased. In fiowing electrolyte through the gap in the process described herein, the maximum flow rate or conditions of flow will be that which causes excessive turbulence within the reaction zone equivalent to the diffusion film thickness.

FIG. 1 is a drawing of a machine for electrolytic grinding in which the present electrolyte solutions may be used. In particular, the machine employs a cathode disk rotatable in a horizontal plane. The cathode disk is aflixed to a rigid electrically insulated spindle driven by a suitably powered motor, preferably having variable speed so that the spindle can be rotated at speeds up to 10,000 rpm. or more. A universal vise is mounted in position so that the part to be ground and held thereby can be advanced toward or retracted from the surface of the disk and can be moved in a direction parallel with a radius of the disk and in addition can be moved in a direction substantially parallel with the plane of the disk. The machine is also provided with a liquid circulating system for introducing the electrolyte to the surface of the disk and for collecting the overflow so it can be kept in continuous circulation by means of a suitable pump. The machine has a hood enclosing the grinding area in a manner that enables the operator to observe the operations. Having thus described in general terms the principal components of the machine and their respective functions, the following description will now identify, in detail, by appropriate reference characters, the various elements of the machine as illustrated in FIGS. 1, 2 and 3.

1 is the spindle on which the cathode disk 2 is carried. 3 is the system for circulating the electrolyte and it comprises a pump 4, a delivery conduct 5 which is terminally provided with a dam 6 held in a predetermined spaced relation with the upper acting face of the cathode disc 2.

While in the preferred embodiment of the invention appropriate means may be provided for the purpose of regulating the gap between the lower edge of the dam and the upper surface of the cathode disk, such adjusting means have been omitted from FIG. 1 for purposes of clarity in the drawing.

The housing 7 has its bottom 8 arranged to slope centrally to a discharge opening 9 which is covered by a baflle plate 10 in spaced relation to the bottom in which the discharge opening is formed. The discharge opening has a return conduit 11 connected therewith, by which the electrolyte is fed back to the pump 4. -If desired, a drain connection generally indicated at 12 may be provided in the return conduit 11 for the purpose of draining the electrolyte from the system. Suitable means may be provided such as a float in the tank or housing for the purpose of maintaining a proper level of electrolyte, i.e., supply of electrolyte in the system.

The electrical panel 13 contains the ampere-minute meter, ammeter and rheostat necessary for adjusting and maintaining the operation by automatic means based on voltage control as hereafter more fully explained.

Spindlev 1 extends upwardly from the cathode disk into a drive housing 14 where it is rotatably supported for high-speed operation. In view of the close tolerances necessary to be maintained between the work which is anodic and the active face of the cathode disk, it is essential that the spindle 1 be so supported that it will not wobble during operation. In the illustrated embodiment of the apparatus, the spindle is driven by means of a remotely mounted motor 15 through a flexible belt 16.

The spindle, at its upper end, may have associated therewith any suitable means such as that illustrated at 17 by which the rotational speed in terms of revolutions per minute of the spindle may be indicated.

Referring now more specifically to FIG. 2 it will be noted that the work piece or anode indicated at 18 is actually a hard metal alloy insert in a drill, the body of which, indicated at 19, is at its opposite end held in a universal vise generally indicated at 20, although any other suitable means may be employed for adjustably supporting the anode in any desired position with respect to the upper surface of the cathode disk 2. Theexternal controls generally indicated at 21 by which the universal vise is adjusted are as illustrated in FIG. 1 conventional, but these may vary also as referred to above.

in order to insure proper circuit characteristics for the electrochemical grinding circuiting, the spindle 1 at its lower end below the disk 2 is provided with a projection generally indicated at 22 which dips into and rotates in a mercury bath contained in cup 23 from which extends a conductor member 24- which terminally carries a lead 25 which will be connected in the same circuit as the lead 26 on the vise member 20.

The cathode disk 2 may have any desired physical dimensions as for example in the machines which have been operated successfully thus far, the cathode disk has had diameters of 8 and 12 inches respective-1y. The only difference which exists when using disks of different diameters is that correspondingly different spindle speeds are necessary in order to maintain the same surface speed on that area of the disk with which the work is adjacent.

The upper surface of the disk may be planar, but preferably it is slightly conical. Preferably, it is the surface of a very flat right cone. When a conical surface is thus used the elements of the cone should slope upwardly at an angle of about 1. For certain purposes such as when employing an electrolyte of certain viscosity or when forming a surface on the work which is other than flat, that is, contour grinding or for a variety of other reasons, the shape of the upper surface of the cathode may vary from that of a right cone.

It is essential for most purposes that the electrolyte supporting surface of the cathode be as smooth as prac- 17 tical in order that the film may be distributed thereover with a minimum turbulence.

Since the path of the electrolyte film issuing from beneath the dam 6 is a resultant of its circumferential and radial progression, for certain types of operations it is desirable to orient in a particular way the surface of the work piece contacting the electrolyte film. Thus, it has been found that when operating at the higher voltages such as in the vicinity of 25 volts, and if a sharp cutting edge is desired, the work should be oriented so that such edge occurs on that side of the tool facing upstream and that the line representing the cutting edge be substantially at right angles to the direction of relative movement between the film and work piece.

The present method is characterized by the employment of current densities considerably higher than the prior art processes referred to previously. For the purpose of maintaining such current density dilferent voltage levels are required depending on the thickness and other characteristics of the electrolyte film. When utilizing electrolytes of the character referred to herein, it has been found that for the purpose of utilizing 25 volts, the electrolyte film has a thickness such that whereas there is substantially no turbulence in the area where the film meets the work and that edge is accordingly made sharp, in the area where the film leaves the work there is sufficient turbulence so that the edge is less sharp.

When, however, the film thickness is reduced so as to require only volts, for the same current density, the film becomes so thin that the turbulence thereof is very substantially reduced and under such conditions of operation the leading edge of the work is made even more sharp than when utilizing a thicker film and a higher voltage and the trailing edge of the work, at the lower voltage level conditions of operation, is also relatively sharp, that is, the trailing edge of the work under 5-volt operative conditions has been found to be sharper than the leading edge under 25-volt operative conditions.

The factors just discussed signify the essential difference between the process of the described machine and the processes of the prior art, for example, those wherein the cathode carries projections which extend into or through the film in substantial contact with the work for the purpose of, for example, removing from the work surfaces the films formed thereon by the electrochemical action.

In view of the fact that the cutting speeds which can be achieved by the use of this technique are substantial, and the further fact that for best operations, the space between the cathode and anode are relatively small, it becomes important to provide some means for adjusting such spacing. It is possible to effect such adjustment manually by means of the controls illustrated, for example, at 21 in FIG. 1 for the reason that under fixed operating conditions a definite relationship exists between the current density, cutting rate and gap distance. The anode feed rate is the independent variable which determines the gap distance, current density and cutting rate. At equilibrium grinding conditions, the cutting rate is equal to the anode feed rate and the current density and gap distance have fixed values. If the anode-feed rate is increased slightly above the cutting rate, the gap decreases, the current density increases, and the cutting rate increases until it equals the increased anode-feed rate. When equilibrium conditions have been re-established at the higher anode-feed rate, the gap is smaller and the current density is higher. If the anode-feed rate is decreased slightly below the cutting rate, the gap increases, the current density decreases and the cutting rate decreases until it equals the reduced anode-feed rate. When equilibrium conditions have thus been re-established at the lower anodefeed rate, the gap is larger and the current density is smaller. The above examples show that once the anodefeed rate is set, the electrolytic process is inherently selfcorrecting. It is thus possible to operate under this method by controlling the feed rate manually after some experience has been had along this line. The self-correcting tendency just explained will tolerate rates of feed which, when controlled manually, are either not at the maximum or are of a varying nature within limits. For most consistent results, however, it is desirable that some means be provided which are functionally responsive to one of the variables referred to and which will automatically maintain a feed rate which bears a predetermined proportional relation to such variable. For example, since the thickness of the film or more accurately the space between the anode and cathode when varied is reflected in substantial changes in current values at a uniform voltage, means, as described in Serial No. 577,015, which are functionally responsive to variations in current can be used for the purpose of maintaining the feed at a constant rate.

Simply pouring the electrolyte at the not quite touching conjunction of the rotating disk cathode and the article being ground, as is done by pumping the oil-emulsion coolant and lubricant out of a tube so a stream strikes the grinding wheel where it touches the article being ground in conventional abrasive wheel grinding machines and in electrolytically assisted grinding wheels described in the literature, is not suitable for electrolytic grinding when performing the method of the machine shown in FIG. 1. In this case, a thin coating of electrolyte is metered onto the disk surface by a deflecting dam. The clearance of the dam above the disk and the rota tional speed of the disk are such that the electrolyte is firmly impacted against the disk by centrifugal force until after it has passed under the article being electrolytically ground or cut. This force is believed to so condition the film of electrolyte on the disk that substantially no tur-' bulence occurs in the electrolyte film as it passes through the gap between the disk and the article being ground. Such absence of turbulence is believed confirmed by the fact that flat surfaces without waviness and with sharp edges result from the anodic dissolution that effects anodic grinding. Turbulence, if present in the electrolyte film, would be accompanied by waivness or flow patterns formed in the ground surface. FIG. 1 shows the disk in a substantially horizontal position, but the useful apparatus is not limited to such an arrangement. The plane of the disk may be vertical or at an angle.

An important part of the novelty in one form of the method of the present invention resides in this demon strationthat an electrolyte having sufficient degree of solubility for metal oxides can be deposited, practically rigidized in stream-line, non-turbulent flow on a rotating disk, and that a metal or other electrically conducting article brought into the outermost layer of this electrolyte can be made anodic with direct current at low voltage and much higher-than-usual current density known in the art as a result of which highly effective and efficient electrolytic grinding can be done at rates at least equal to and usually exceeding the rates of electrolytijcally assisted abrasive methods, electric discharge methods, and of conventional abrasive methods. v

Since no metal removal occurs until the article to be ground contacts the electrolyte film, easy and simple operation results. Since the right gap is adjusted by metering the electrolyte film, the article is automatically spaced correctly when electrolysis current flows, since no action can occur until the electrolyte is contacted upon advancing the article toward the electrolyte.

Although a rotating cathode disk having a flat surface radially from center to outer rim can be used in performing the method of this invention, the preferred apparatus utilizes a rotating cathode disk that is concave at the center. The preferred concavity is provided with 0.002 to 0.100 inch thinner in section at the center than at the outer rim of the grinding face, decreasing radially in a straight line to zero at the outer rim or with a 5 to 40 degree bevel at the outer edge. This concavity adds a component of centrifugal force in a better manner to impact the electrolyte against the disk surface. By the means provided according to FIG. 1 and described herein-before, non-turbulent electrolyte films can be easily maintained in thicknesses less than 0.008 inch. At a given applied voltage, the amperage that can pass is greater per unit of area the thinner the electrolyte film and thus the closer the article is to, but not, touching the cathode disk.

For accomplishing electrolytic grinding as disclosed by the apparatus of FIG. 1, wheel speeds (cathode disk speed) are those at which a uniform uninterrupted smooth film of electrolyte is formed at point of discharge of the electrolyte from the circulating pump to the location behind the metering dam. Generally, wheel speeds will be in the range of 2000 to 15,000 feet per minute, depending on the viscosity of the electrolyte. More specifically, speeds of 6000 to 10,000 feet per minute are preferred.

In general, current density on the article (as anode) to be electrolytically ground will be 100 to 2000 amperes per square inch. More specifically, 500 to 1600 amperes per square inch are preferred.

Electrolyte film thickness (anode-to-cathode gap) will be 0.0001 to 0.020 inch. More specifically, film thickness in the range of 0.001 to 0.008 inch are preferred, depending on the composition of electrolytic solution being used, the metal being electrolytically ground, and the voltage being used, as for rough cut or fine finishing.

Operating voltages will generally be in the range of 2 to 30 volts. More specifically, voltages of 5 to volts should be used for practical electrolytic grinding rates.

The material of the cathode disk is not important so long as it has adequate electrical conductance and resistance to chemical attack in the electrolyte and is not dainaged by hydrogen discharge.

Other advantages of the method of this invention will be apparent to those skilled in the art of electrolysis and of metal grinding,.machining and shaping. For example, electrolytic grinding is accomplished without generation of damaging heat in the article to be ground or pressure on the article to be ground and, being in addition without physical contact, cannot introduce damaging stresses in the surface of hardened steels; cannot leave torn, fragmented, damaged metal on a surface such as results from the ripping, shearing, tearing and smearing by which abrasives and contact tools cut; cannot deform thin-section metal parts; and is not hampered by plastic flow of soft metals that fill abrasive wheels and smear under contactcutting tools.

Throughout the preceding description reference has been made to the employment of a disk 2 as the cathode on which the electrolyte is supported and to which electrolyte film the work to be electrolytically formed is presented. In FIG. 4 there is shown an alternative arrangement wherein a rotating spindle carries a disk 31 having a substantially cylindrical flange 32 integral therewith. The electrolyte is introduced through conduit 34 and distributed by the dam or bafile 35 on the end of the conduit. The work piece to be electrolytically formed is indicated generally at 36 and is held by a suitable arm 37 by which it may be presented to the electrolyte film in the manner previously described in connection with FIGS. 1, 2 and 3.

Adjustment of anode-cathode spacing One simple means by which this can be accomplished is illustrated in FIG. 7 wherein 40 designates the direct current control circuit power source, 41 is a rheostat for the control of the speed of a variable speed reversing motor 42, the direction of rotation of which is controlled by the reversing switch 43. The shaft of the motor 42 is connected through a gear box 44 to a gear 45 on the adjusting stem 46 of the universal vise 47, the arm 48 of which carries the work piece 49 in the proper spaced relation to the disk 50. 51 detnotes the DC power source for the work circuit, 52 is the rheostat by which that circuit is controlled and 53 is the switch by means of which the circuit is energized and deenergized.

Electrolytic grinding without the arcing, sparking or scraping as in the prior art is inherently self-adjusting. If the feed rate tends to exceed the cutting rate, the gap will decrease, causing the current density to increase, and the cutting rate will increase to a value equal to the feed rate. Conversely, if the cutting rate tends to exceed the feed rate, the gap will increase causing the current density to decrease, and the cutting rate will decrease to a value equal to the feed.

Anode feed can be accomplished by the variable speed motor 42 with the gear reduction train 44 to allow feed rates covering the range of cutting rates achieved in electrolytic machining (that is, 0 to 0.2 inch or more per minute). The reversing switch 43 is provided to Withdraw the work 49 from the cathode disc 50 when the metal removal operation is completed. This reversing switch can be manually controlled by the operator or can be operated by an electric timer with variable settings, or by other means, according to need for timing the duration of the electrolytic grinding, as described below. As shown in FIG. 7, a separate switch 53 is provided for the electrolysis grinding circuit. Alternatively, the reversing switch mechanism could be arranged to simultaneously open or close the electrolysis grinding circuit.

There are several methods of terminating the cutting action after the desired amount of metal removal. The choice will depend on the requirements of the machining operation.

The following examples illustrate the unique control features possible for electrolytic machining with present- -anode-feed-rate control:

(1) Cutting action can be terminated by an adjustable limit switch which is mechanically activated by the anode feed holder. The limit switch would simultaneously open the electrolysis circuit and reverse the feed direction. The advantage of this method is that the limit switch can be set with reference to the cathode disk. No further adjust ment of the limit switch setting would be required in repetitive machining operations, since there is no wear on the cathode disk. In conventional machining or other electrolytic processes, tool wear or cathode-disk wear must be continually compensated by some means in order to achieve reproducible accuracy.

(2) An electric timer could be set in conjunction with the preselected feed rate, so as to terminate the cutting action after the desired anode feed travel from the initial position. At the end of a specified time, the electric timer can activate the mechanism for opening of the electrolysis circuit and reversing of the feed direction.

(3) Similar to 2, except that the start of the electric timer would be activated by the start of the electrolysis current. In this manner, the timing of the depth of cut can be started when the anode entered the electrolyte. The advantage of this method is that by suitable choice of time and feed rate, a definite depth of cut can be obtained independent of the initial positioning of the anode in the holder.

(4) For precision work on a production basis of a number of similar parts of known anode area, an ampere-minute meter connected in the electrolysis circuit will control and limit the electrolytic grinding. The cutting action can be terminated after a predetermined number of ampere minutes of electricity have passed. As an example, assume an anode area of 0.1 square inch and a cutting rate of about 0.050 inch per minute at 1000 amperes per square inch. In cutting 0.050 inch, -ampere minutes will pass. With an ampere-minute meter sensitive to the nearest tenth of an ampere minute, the precision of cut will be 000005 inch.

In operation, the desired anode-feed rate and electrol ysis voltage are selected. The electrolysis circuit is closed, and the anode feed toward the cathode disk is begun. As the work enters the electrolyte, current flows, and metal 21 removal begins. At the gap distance set, the cutting rate will be less than the anode-feed rate; therefore, the gap will tend to decrease, the current density will increase, and the cutting rate will increase, until the cutting rate equals the feed rate.

It is also contemplated to provide a voltage-control unit. This consists of a voltage divider to select from the line voltage the desired electrolysis voltage. During electrolysis, the equilibrium gap spacing that exists when the feed rate equals the cutting rate can be controlled by the electrolysis voltage. The gap for electrolytic grinding, as described herein, varies directly with the electrolysis voltage. The electrolysis voltage is selected so that the equilibrium gap distance is less than the electrolyte film thickness on the cathode disk, but large enough to prevent arcing or sparking.

FIGURE 8 shows the general relationship between current density, cutting rate and gap spacing at various voltages, as characteristic of electrolytic machining as described herein. The exact numeral values and relationships will depend on many factors, i.e., the type of anode material, the electrolyte, etc. In FIG. 8, a straight-line relationship between gap distance and current density is shown for simplicity. The important factor is that the current density varies inversely to the gap spacing for the purposes of gap control during electrolytic machining. A straight-line relationship is not essential.

This control system, based on a preselected cutting rate, is advantageous because the method is independent of the anode area being machined. This control system does not require auxiliary electronic equipment. It is apparent that such a simple control system can only be used for electrolytic machining without scraping, sparking or arcing. Such a control system would not be feasible if continual contact of the anode and cathode were required during electrolysis.

Other forms embodying the features of the invention may be employed, change being made as regards the features herein disclosed, provided those stated by any of the following claims or the equivalent of such features be employed.

We therefore particularly point out and distinctly claim as our invention:

1. A universal multi-component electrolyte for the electrolytic removal of stock from a metallic workpiece selected from the group consisting of steel, a cemented metal carbide, silver solder, and composite workpieces of at least two of said metals, characterized in that said multi-component electrolyte consists essentially of an aqueous alkaline solution of an ionizable hydroxide for solubilizing the oxide formed from the metal of said metal carbide, a water-soluble salt of a saturated polybasic aliphatic organic acid for solubilizing the cementing agent of the cemented metal carbide, a water-soluble compound furnishing the chloride ion for the electrolytic dissolution of steel, and a silver solubilizer selected from the group consisting of sodium cyanide, ethylene diamine, and tetrasodium ethylenediaminetetraacetate.

2. In the method of electrolytically removing stock from a composite workpiece, including steel and a carbide body having a metallic cementing matrix, without contacting the workpiece with a rigid forming or scraping tool; the improvements comprising contacting such workpiece with at least a tri-component electrolyte consisting essentially of an aqueous alkaline solution of an ionizable hydroxide, a water-soluble compound furnishing a halogen ion, and a water-soluble solubilizing agent for the metallic cementing matrix selected from the group consisting of a salt of a saturated polybasic aliphatic organic acid, an ammonium halide, and an alkaline amine; applying a direct current voltage between said workpiece and electrolyte with the workpiece as the anode; carrying a resultant direct current substantially by said ionizable hydroxide while simultaneously dissolving by such hydroxide the metal of said carbide removed from the body at a rate at least equal to its rate of electrolytic removal to prevent the formation of water-insoluble compounds of said carbide metal; and simultaneously dissolving said metallic cementing matrix by the defined water-soluble solubilizing agent and dissolving the steel by said watersoluble halogen compound also at rates at least equal to their respective rates of electrolytic removal to prevent the formation of water-insoluble compounds of either of said matrix metal and steel.

3. The method of claim 2 wherein the water-soluble alkaline amine is selected from the group consisting of triethanolamine, ethylene diamine, and tetrasodiurn ethylenediaminetetraacetate.

4. The method of claim 2 wherein the cemented carbide body is cobalt-cemented tungsten carbide.

5. In the method of electrolytically removing stock from a composite workpiece, including steel soldered to a carbide body having a metallic cementing matrix, without contacting the workpiece with a rigid forming or scraping tool; the improvements of dissolving all of such metals at substantially the same rates comprising contacting such workpiece with a tetra-component electrolyte consisting essentially of an aqueous alkaline solution of an ionizable hydroxide, a water-soluble compound furnishing a halogen ion, a solder-dissolving agent selected from the group consisting of ethylene diamine and tetrasodium ethylene diamine tetraacetate, and a water-soluble solubilizing agent for the metallic cementing matrix selected from the group consisting of a salt of a saturated polybasic aliphatic organic acid, an ammonium halide, and an alkaline amine; applying a direct current voltage between said workpiece and electrolyte with the workpiece as the anode; carrying a resultant direct current substantially by said ionizable hydroxide while simultaneously dissolving by such hydroxide the metal of said carbide removed from the body at a rate at least equal to its rate of electrolytic removal to prevent formation of water-insoluble compounds of said carbide metal; and simultaneously dissolving said metallic cementing matrix, the steel, and the soldering metal by, respectively, the defined water-soluble solubilizing agent, the water-soluble halogen, and the solder-dissolving agent also at rates at least equal to their respective rates of electrolytic removal to prevent the formation of water-insoluble compounds of any of said matrix metal, steel, and soldering metal.

6. In the method of electrolytically removing stock from a composite workpiece, including steel and a carbide body having a metallic cementing matrix, without contacting the workpiece with a rigid forming or scraping tool; the improvements comprising contacting such workpiece with at least a tri-component electrolyte consisting essentially of an aqueous alkaline solution of an ionizable hydroxide, a water-soluble compound furnishing a halogen ion, and a water-soluble solubilizing agent for the metallic cementing matrix consisting esesntially of an agent furnishing ammonium and halide ions in said aqueous solution; applying a direct current voltage between said workpiece and electrolyte with the workpiece as the anode; carrying a resultant direct current substantially by said ionizable hydroxide while simultaneously dissolving by said hydroxide the metal of said carbide removed from the body at a rate at least equal to its rate of electrolytic removal to prevent the formation of water-insoluble compounds of said carbide metal; simultaneously forming a water-soluble complex with said metallic cementing matrix by the defined ammonium and halide ions at a rate at least equal to its rate of electrolytic removal to prevent the formation of water-insoluble compounds of the matrix metal, and simultaneously dissolving the steel by said water-soluble halogen compound also at a rate at least equal to its rate of electrolytic removal similarly to prevent the formation of water-insoluble compounds of the steel.

7. The method of claim 6 wherein said solubilizing agent is ammonium chloride.

8. The method of claim 6 wherein the compound furnishing the halogen ion is selected from the group consisting of sodium chloride, ammonium chloride, potassium chloride, and lithium chloride.

9. In the method of electrolytically removing stock from a composite workpiece, including steel and a carbide body having a metallic cementing matrix, without contacting the workpiece with a rigid forming or scraping tool; the improvements comprising contacting such workpiece With at least a tri-component electrolyte consisting essentially of an aqueous alkaline solution of an ionizable hydroxide, a water-soluble compound furnishing a halogen ion, and a water-soluble solubilizing agent for the metallic cementing matrix selected from the group consisting of a tartrate, at citrate, an oxalate, and a gluconate; applying a direct current voltage between said workpiece and electrolyte with the workpiece as the anode, carrying a resultant direct current substantially by said ionizable hydroxide While simultaneously dissolving by such hydroxide the metal of said carbide removed from the body at a rate at least equal to its rate of electrolytic removal to prevent the formation of water-insoluble compounds of said carbide metal; and simultaneously dissolving said metallic cementing matrix by the defined Water-soluble solubilizing agent and similarly dissolving the steel by said water-soluble halogen compound also at rates at least equal to their respective rates of electrolytic removal to prevent the formation of Water-insoluble compounds of either of said matrix metal and steel.

10. In the method of electrolytically removing stock from a composite workpiece, including steel and a carbide body having a metallic cementing matrix, without contacting the workpiece with a rigid forming or scraping tool; the improvements comprising contacting such Workpiece with at least a tri-component electrolyte consisting essentially of an aqueous alkaline solution of an ionizable hydroxide, a water-soluble compound furnishing a halogen ion, and a water-soluble solubilizing agent for metallic cementing matrix selected from the group consisting of triethanolamine, ethylene diamine, and tetrasodium ethylenediaminetetraacetate; applying a direct current voltage between said workpiece and electrolyte with the workpiece as the anode; carrying a resultant direct current substantially by said ionizable hydroxide while simultaneously dissolving by such hydroxide the metal of said carbide removed from the body at a rate at least equal to its rate of electrolytic removal to prevent the formation of water-insoluble compounds of said carbide metal; and simultaneously dissolving said metallic cementing matrix by the defined water-soluble solubilizing agent and dissolving the steel by said water-soluble halogen compound also at rates at least equal to their respective rates of electrolytic removal to prevent the formation of waterinsoluble compounds of either of said matrix metal and steel.

References Cited UNITED STATES PATENTS 1,337,718 4/1920 Mason 204 1,598,731 9/1926 Lee 204-145 2,615,840 10/1952 Chapman 204-145 2,915,444 12/1959 Meyer 204-145 2,939,825 6/1960 Faust et a1 204--142 2,939,826 6/1960 Gulick 204145 2,385,198 9/1945 Engle 204143 2,826,540 3/1958 Keeleric 204-143 2,649,361 8/1953 Leipzig 4142 2,429,107 10/1947 Petren 101149.2 1,863,868 6/1932 McCullough 204146 2,915,444 12/1959 Meyer 204145 2,299,054 10/1942 Harshaw 204141 2,615,840 10/1952 Chapman 204141 2,863,811 12/ 1958 Ruscetta 204141 FOREIGN PATENTS 164,476 10/ 1953 Australia.

ALLEN B. CURTIS, Primary Examiner.

JOHN H. MACK, JOHN R. SPECK, WINSTON A.

DOUGLAS, Examiners.

P. SULLIVAN, R. GOOCH, Assistant Examiners, 

1. A UNIVRSAL MULTI-COMPONENT ELECTROLYTE FOR THE ELECTROLYTE REMOVAL OF STOCK FROM A METALLIC WORKPIECE SELECTED FROM THE GROP CONSISTING OF STEEL, A CEMENTED METAL CARBIDE,SILVER SOLDER, AND COMPOSITE WORKPIECIES OF AT LEAST TWO OF SAID METALS, CHARACTERIZED IN THAT SAID MULTI-COMPONENT ELECTOLYTE CONSISTS ESSENTIALLY OF AN AQUEOUS ALKALINE SOLUTION OF AN IONIZABLE HYDROXIDE FOR SOLUBILIZING THE OXIDE FORMED FROM THE METAL OF SAID METAL CARBIDE, A WATER-SOLUBLE SALT OF A SATURATED POLYBASIC ALIPHATIC ORGANIC ACID FOR SOLUBILIZING THE CEMENTING AGENT OF THE CEMENTED METAL CARBIDE,A WATER-SOLUBLE COMPOUND FURNISHING THE CHLORIDE ION FOR THE ELECTROLYTIC DISSOLUTION OF STEEL, AND A SILVER SOLUBLIZER SELECTED FROM THE GROUP CONSISTING OF SODIUM CYANIDE, ETHYLENE DIAMINE, AND TETRASODIUM ETHYLENEDIAMINETETRAACETATE.
 2. IN THE METHOD OF ELECTROLYTICALLY REMOVING STOCK FROM A COMPOSITE WORKPIECE, INCLUDING STEEL AND A CARBIDE BODY HAVING A METALLIC CEMENTING MATRIX, WITHOUT CONTACTING THE WORKPIECE WITH A RIGID FORMING OR SCRAPING TOOL; THE IMPROVEMENTS COMPRISING CONTACTING SUCH WORKPIECE WITH AT LEAST A TRI-COMPONENT ELECTROLYTE CONSISTING ESSENTIALLY OF AN AQUEOUS ALKALINE SOLUTION OF AN IONIZABLE HYDROXIDE, A WATER-SOLUBLE COMPOUND FURNISHING A HALOGEN ION, AND A WATER-SOLUBLE SOLUBILIZING AGENT FOR THE METALLIC CEMENTING MATRIX SELECTED FROM THE GROUP CONSISTING OF A SALT OF A SATURATED POLYBASIC ALIPHATIC ORGANIC ACID, AN AMMONIUM HALIDE, AND AN ALKALINE AMINE; APPLYING A DIRECT CURRENT VOLTAGE BETWEEN SAID WORKPIECE AND ELECTROLYTE WITH THE WORKPIECE AS THE ANODE; CARRYING A RESULTANT DIRECT CURRENT SUBSTANTIALLY BY SAID IONIZABLE HYDROXIDE WHILE SIMULTANEOUSLY DISSOLVING BY SUCH HYDROXIDE THE METAL OF SAID CARBIDE REMOVED FROM THE BODY AT A RATE AT LEAST EQUAL TO ITS RATE OF ELECTROLYTIC REMOVAL TO PREVENT THE FORMATION OF WATER-INSOLUBLE COMPOUNDS OF SAID CARBIDE METAL; AND SIMULTANEOUSLY DISSOLVING SAID METALLIC CEMENTING MATRIX BY THE DEFINED WATER-SOLUBLE SOLUBILIZING AGENT AND DISSOLVING THE STEEL BY SAID WATERSOLUBLE HALOGEN COMPOUND ALSO AT RATES AT LEAST EQUAL TO THEIR RESPECTIVE RATES OF ELECTROLYTIC REMOVAL TO PREVENT THE FORMATION OF WATER-INSOLUBLE COMPOUNDS OF EITHER OF SAID MATRIX METAL AND STEEL. 